This is a request for an ADAMHA Research Scientist Development Award, Level II. The goal of this proposal is to determine the role of the endogenous opioid peptides B-endorphin and dynorphin in the perception and modulation of pain stimuli. Pharmacological, biochemical and binding studies will be carried out in three major areas of the nervous system known to be involved in pain perception: the periaqueductal gray (PAG); rostroventral medulla (RVM); and the dorsal horn of the spinal cord. We will determine the ability of dynorphin administered intrathecally to modulate analgesia induced by morphine and other opioids. Levels of dynorphin in the spinal cord will be quantitated in animals treated acutely or chronically with morphine or other opioids. Binding sites for B-endorphin and dynorphin in these areas will be identi- fied by determining the ability of these peptides, and their fragments, to compete with opioid ligands selective for mu, delta and kappa receptors; competition experiments using tritiated B- endorphin and dynorphin and unlabelled mu, delta and kappa opioids will also be carried out. An attempt will be made to purify B- endorphin and dynorphin receptors by cross-linking the tritiated peptides to their receptors, and isolating the resulting complexes by SDS gel electrophoresis. The ability of these receptors to cross-react with antibodies to purified mu receptors will be determined.